WO2008135367A1

WO2008135367A1 - Device for the capacitive measurement of the quality and/or degradation of a fluid, including a capacitive sensor that is mechanically decoupled from the encapsulation element thereof

Info

Publication number: WO2008135367A1
Application number: PCT/EP2008/054745
Authority: WO
Inventors: Gérald Chambon
Original assignee: Alpsens Technologies Inc.
Priority date: 2007-04-20
Filing date: 2008-04-18
Publication date: 2008-11-13
Also published as: US8436629B2; EP2142916B1; ES2693231T3; EP2142916A1; US20100176819A1; CH715650B1

Abstract

The invention relates to a device for the capacitive measurement of the quality and/or degradation of a fluid, including a sensor encapsulated in a perforated casing, in which the sensor is connected to the encapsulation element such as to be mechanically decoupled from same.

Description

CAPACITIVE MEASUREMENT PROVISION FOR QUALITY AND / OR

DEGRADING A FLU I HAVING A SENSOR

CAPACITIVE MECHANICALLY DECOUPLED FROM SOUND

Encapsulation

The present invention relates to a capacitive measuring device for the quality and / or the degradation of a fluid, particularly an oil. The invention particularly relates to such a device comprising a capacitive sensor for measuring the quality and / or degradation of a frying oil, directly disposed in the cooking appliance, and wherein the capacitive sensor encapsulated in a protective case fixed in a submerged area of the vessel of the cooking apparatus is decoupled mechanically from its encapsulation.

It is well known that edible oils degrade during cooking, especially when they are repeatedly worn at high temperatures. Typically, for frying food these oils are brought to temperatures of the order of 180 ° C. At these temperatures occur a multitude of chemical reactions, such as polymerizations, thermo-oxidations, etc., which significantly alter the quality of the oil. The quantity of certain products of these reactions must not exceed a threshold imposed by the legislation, because beyond this threshold the oil is considered unfit for consumption. It is therefore important to be able to detect this threshold reliably in order to replace the oil as soon as it is necessary. For a long time this moment was left to the appreciation of the cooks who following a visual inspection and / or olfactory determined if the oil was still fit for consumption. Of course, such a method is purely subjective and is therefore not reliable. A device for capacitively measuring the quality and / or the degradation of a cooking oil has been proposed in patent EP 1 588 158 to overcome these disadvantages. The contents of this patent are incorporated herein by reference. In this device, the capacitive sensor is directly disposed in the vessel of the cooking apparatus, this sensor being encapsulated in a perforated protective housing fixed in a submerged zone of the vessel.

Although the device described in this patent application works satisfactorily, the fact remains that the measurement of capacity inside a fryer is a very sensitive operation. Indeed, the variation of a few picofarads between new oil and used oil, strongly influenced by temperature, water and impurities is not easy to detect. To this is added the operation of the device in a very hard environment in which the capacitive sensor, and if necessary the temperature sensor with which it is associated, are subjected to high temperatures above 200 ° C., to shocks when Careless operators hit the sensor with the baskets receiving the food to be fried.

The protection of the capacitive sensor, and if necessary that of the temperature sensor with which it is associated, is therefore an extremely important problem that should be addressed in order not to deteriorate the accuracy of the measurements and to impair the lifetime of the device. because these measures depend directly on it.

The aim of the invention is thus to remedy this problem by providing a device for capacitive measurement of the quality and / or the degradation of a fluid comprising a sensor encapsulated in a perforated housing in which the sensor is connected to said encapsulation of to be decoupled mechanically from it.

The invention therefore focuses on the decoupling between the capacitive sensor - relatively fragile, assembled and precisely aligned - and its encapsulation. The function of the latter is to better protect the sensor in the following situations:

In oil, in normal use: protect against shocks of the baskets while allowing an optimal circulation of the oil as well as shocks due to any other instrument

Out of tank for cleaning: protection against falls, shocks in the washing machine, transport, ...

The mechanical decoupling of the sensor and its encapsulation makes it possible to increase the reliability rate (fewer parts under stress), to extend the life of the sensor and to simplify assembly. Another advantage lies in the separation of measurement functions and encapsulation functions, which allows: to subcontract part of the system (encapsulation) while keeping control of the assembly process of the sensor. - to make changes to one or other of the parties without affecting the other. to simplify a large part of the encapsulation parts by significantly reducing the stresses on the encapsulation and therefore also the costs: - materials: thermal stability and mechanical stress less important machining tolerances smaller because the alignment does not need to be optimal.

Other features and advantages of the present invention will appear in the following description of a preferred embodiment of a measuring device according to the invention, presented by way of non-limiting example with reference to the accompanying drawings, in which: - AT -

Figure 1 is a schematic sectional view of a fryer tank in which a measuring device with its encapsulated sensor according to the invention can be mounted;

FIG. 2 is a schematic view of the encapsulated sensor of the device according to the invention

FIG. 3 is a schematic perspective view partially broken away of the encapsulated sensor of the device according to the invention

Figure 4 is a schematic sectional view of the encapsulated sensor according to the invention; - Figure 5 is a schematic elevational view of the sensor according to the invention on which an encapsulation plate has been omitted;

Referring firstly to Figure 1, we see an embodiment of a capacitive measuring device of the quality and / or degradation of a fluid including an oil, designated by the general reference 1 .

Note that the following description will be made in an application of the device 1 to the measurement of the quality and / or degradation of a food oil or the like, used to fry food in a cooking apparatus comprising a tank 2 in which oil can be heated typically up to about 200 ° C.

The measuring device 1 comprises an encapsulated sensor 4 comprising a pair of electrodes 6, 8 spaced from one another and intended to be immersed in a fluid F (FIG. 2), for example the oil of a fryer. , whose quality and / or degradation is to be measured and whether it is still fit for use. The electrodes 6, 8 form with the oil F a capacitive measuring element EFM whose capacity varies as a function of the dielectric constant of the oil. As the oil degrades, the amount of polar compounds present therein increases and leads to an increase in its dielectric constant. Thus, by measuring the evolution of the capacitance of the capacitive measuring element EFM, the degree of quality and / or degradation of the oil can be determined. The sensor 4, and more precisely its capacitive element EFM, is able to provide an electrical output signal representative of the dielectric constant of the oil over a wide temperature range, in particular between 20 ° C and 200 ° C. The electrical signal is processed by an electronic processing circuit 10 disposed outside the tank 2. The sensor 4 is connected to the electronic processing circuit by electrical contacts 4a. The sensor is for example removably attached under the heating body 12 by means of a fastening and connecting support 14 integral with the latter. Typically the sensor 4 can plug into the support 14 by its electrical contacts 4 which are for example shaped resilient clamps. The fixing and connecting support 14 is connected to the electronic circuit by means of protected cables 16, for example in tubes. Each electrode 6, 8 of the pair has the shape of a comb having a plurality of teeth 6a, 8a substantially parallel to each other and extending from a base 6b, 8b. The electrodes 6 and 8 are arranged relative to each other so that the teeth 6a of an electrode 6 are nested between the teeth 8a of the other electrode 8. The teeth of the electrodes 6 and 8 are thus arranged substantially in the same plane.

It will be noted in this connection that the electrodes 6 and 8 are for example formed from the same plane plate cut in an appropriate manner, the plate being sufficiently rigid so that the electrodes retain their shape when they are manipulated. In the example described, the electrodes are made from a food steel plate (austenitic stainless steel type 18-10 low carbon) having a thickness of between 0.1 and 3 mm. Other types of food steels may also be used, for example Z7CN18-09, Z3CND18-12-02, Z6CNDT17-12 and Z7CNU16-04. The plate is cut by means of a laser beam, which makes it possible to produce between the teeth of the electrodes gaps between 10 nm and 1 mm. It is understood that more the gap is small, the sensitivity of the capacitive element is high. According to an alternative embodiment, it is also conceivable to produce electrodes formed of a substrate coated with a conductive material, for example a substrate coated with a platinum gold layer or the like. The electrodes 6 and 8 are arranged in a perforated encapsulation box. This housing is formed of plates 18, 29 perforated metal plates between which the electrodes 6, 8 with interposition at the ends of two pairs of spacers 22a, 22b and 24a, 24b of insulating material between which the electrodes 6, 8 forming the impedimetric probe are sandwiched. The electrodes 6, 8 are fixed plates 18, 20 via the spacers 22a, 22b at one end and are guided free in the spacers 24a, 24b at their opposite end.

The perforations of the plates 18, 20 of the encapsulation are arranged facing the measurement region of the electrodes 6 and 8, that is to say facing the air gaps defined by the spaces between the teeth 6a of the electrode 6 and the teeth 8a of the electrode 8. With this configuration, the fluid to be measured, in this case the oil, bathes the two faces of the electrodes 6 and 8 on either side of the plane of these electrodes so it can come to circulate in the vicinity of the teeth 6a and 8a of the electrodes 6 and 8.

This encapsulation structure of the electrodes makes it possible to optimize the circulation of the oil around the two faces of the planar electrodes and in particular to create two channels C1, C2 defined respectively between a first surface of the electrodes 6, 8 and the perforated plate 18 and a second surface of the electrodes 6, 8 opposite to the first and the perforated plate 20.

The fixing of the electrodes 6 and 8 to the spacers is carried out by resilient means, namely by two spring blades 26, 28 also ensuring the function of electrical contact between the electrodes and contact elements 4a of the sensor 2. By this elastic fixation, the sensor is mechanically decoupled from its encapsulation box. These blades, cut in a sheet of stainless steel of 100 microns thick by electro-erosion, ensure the elastic positioning of the probe in the encapsulation box. The probe is guided in the direction perpendicular to the plane of the plates 18 and 20 by fixing elements 30a, 30b which are housed in bores of the spacers 24a, 24b. A small clearance is left so that the probe is "free" in the direction perpendicular to the plane of the plates 18 and 20 in its location, resting simply on the insulating parts. The spacers are preferably made of a material resistant to temperatures between 20 ° C and 200 ° C and having a low coefficient of thermal expansion, such as a ceramic material. However, they can be made of any other insulating material compatible with the application of the measurement device envisaged. As an example for a food application to be stable in the aforementioned temperature range, the spacers could also be made of a fluoropolymer such as Teflon.

Claims

REVEN DI CATIONS

A device for capacitively measuring the quality and / or degradation of a fluid having a sensor encapsulated in a perforated housing in which the sensor is connected to said encapsulation so as to be mechanically decoupled therefrom.

2. Measuring device according to claim 1, characterized in that the mechanical decoupling between the sensor and its encapsulation is carried out by means of two spring blades also ensuring the function of electrical contact between the electrodes of the sensor and the contact elements of the sensor. intended to connect the sensor with the outside.

3. Measuring device according to claim 2 characterized in that the contact elements are shaped resilient clamps.

4. Measuring device according to claim 2 or 3 characterized in that the spring blades ensuring the mechanical decoupling between the sensor and its encapsulation are made of stainless steel and have a thickness of about 100 microns.